The GCLID, short for Google Click Identifier, is a string of characters that Google Ads attaches to the landing page address every time someone clicks an ad. Google's own definition is brief: "Google Click ID (GCLID) is a URL parameter passed with ad clicks," one that "identifies the campaign along with other attributes of the click associated with the ad for ad tracking and campaign attribution," according to the Google Ads Help Center. It exists because a click and a sale usually happen in different places. The ad server records the click; the purchase, form fill or signed contract happens on an advertiser's website or inside a sales team's customer relationship management (CRM) system. The GCLID is the key that lets the two records be joined later.

How a click becomes an identifier

The mechanism starts with a setting called auto-tagging. Google states that it is "required for Google Ads website conversion tracking" and that it "will attach the 'Google Click Identifier' (GCLID) parameter to the URL your customers click," according to its auto-tagging definition. PPC Land's explainer on auto-tagging describes it as a single account-level checkbox, on by default for new accounts and not retroactive.

The sequence runs in five steps. A user clicks an ad on Search, YouTube or another Google surface. Google logs the click server-side and generates a unique value. The browser lands on a URL such as www.example.com/?gclid=123xyz. A Google tag on that page reads the parameter and stores it in a first-party cookie, conventionally named _gcl_aw. When a conversion fires later, the tag sends the stored value back, and Google matches it to the original click, its campaign, ad group, keyword and timestamp.

The value is opaque to the advertiser, and Google notes that it is case sensitive; all the meaning sits on Google's side of the join. That is why the GCLID also underpins the Click Performance report: as far back as September 9, 2013, Danial Klimkin of Google's Ads Developer Relations team wrote that the value was "available to you in the Click Performance Report ... as the 'GclId' field," according to the Google Ads Developer Blog.

Offline conversions and the 90-day horizon

The GCLID matters most where the website is not the end of the journey. A software vendor or insurer may see a lead arrive online and close weeks later by phone. Offline conversion import (OCI) handles this. A hidden form field captures the GCLID when the lead submits a form; the CRM stores it with the lead record; when the deal closes, the advertiser uploads the GCLID, a conversion action name, a conversion time and, optionally, a value.

Google's setup guide stores the identifier in browser storage with a 90-day expiry and describes a click-to-conversion cycle of "less than 14 days or 90 days, depending on the data source," according to the Google Ads Help Center. File-based connectors such as Google Cloud Storage, Amazon S3, HTTP, SFTP and Google Sheets import conversions from the previous 90 days on every run. Salesforce and HubSpot import the last 14 days on the first run. Warehouse connectors, including BigQuery, Snowflake and Redshift, import 14 days each time. PPC Land walked through these steps when Google published a short video explainer on the GCLID on July 16, 2026, including the hidden field named gclid_field used in Google's sample code.

The 90-day figure is the practical ceiling: a sale closing on day 120 cannot be credited to the originating click.

Who handles it

On the buy side, advertisers, agencies, analytics teams and CRM vendors such as Salesforce and HubSpot capture and upload it. On the sell side, Google alone generates and resolves it. No exchange or supply-side platform reads it; it is a closed loop between Google's ad server and the advertiser's destination. The Microsoft Advertising equivalent is the MSCLKID, Meta uses the fbclid and TikTok the ttclid, each tied to its own platform.

Origin and evolution

Google has not published a launch date for the GCLID. AdWords launched in October 2000 and Google Analytics, built on the acquired Urchin product, in November 2005, but neither milestone is documented as the identifier's debut. The 2013 developer post is the earliest dated Google documentation found for this article that describes the field.

The identifier remained stable for more than a decade. Change came from outside. Apple's App Tracking Transparency framework took effect on April 26, 2021, and Google stopped sending the GCLID for iOS 14 traffic from ads on "a handful of Google apps," according to Google. It introduced two replacements: wbraid in March 2021 for web conversions and gbraid in May 2021 for app conversions. Both are aggregated rather than click-level.

Browsers followed. Firefox 102, released in June 2022, began stripping known tracking parameters in strict mode. Mozilla kept an allowlist entry for googleadservices.com, and a Mozilla engineer wrote that "we don't strip gclid in the initial redirect from google.com → googleadservices.com, we still strip it before navigating to the destination page," according to Mozilla's Bugzilla tracker. Apple announced Link Tracking Protection for Safari 17 in June 2023, with a list of about 25 click identifiers including gclid, fbclid and msclkid, according to developer Jeff Johnson as cited by Michael Tsai.

Google itself has also widened the parameter set. gad_source, formerly gad, identifies the traffic source, and gad_campaignid identifies the campaign. Google says these matter "when individual identifiers like gclid and user-provided data are not available," according to its help page on gad_* parameters. Google also said in July 2025 that gclid and gbraid could both be populated in one conversion upload from October 3, 2025, as PPC Land noted in its auto-tagging explainer.

Why it matters for marketers

Every automated bidding strategy in Google Ads depends on conversion data, and for most advertisers the GCLID is the thread connecting that data to spend. If it disappears, the sale still happens but the bidding system never learns of it, and campaigns optimising toward Target CPA (cost per acquisition) or Target ROAS (return on ad spend) then underbid on the queries that work.

Gaps also skew channel comparisons. When Google Analytics receives a session without its paid identifiers, the visit can fall into "(not set)" or "organic." Google added a data-quality alert on July 30, 2026 that flags properties where gbraid or gad_ parameters are missing from URLs that carry a GCLID, as PPC Land reported when Google Ads clicks began losing paid attribution after parameters were stripped.

Limitations, criticisms and disputes

The first limitation is fragility: a URL parameter survives only if every redirect, link shortener and single-page application router passes it intact. The second is the 90-day horizon described above. The third is consent: in the European Economic Area, storing the GCLID in a cookie depends on the ad_storage consent signal, so refusals reduce coverage.

The scale of Safari stripping is genuinely disputed. Testing reported by PPC Land in September 2025 found that iOS 26 had a mixed impact. Frederik Boysen, chief executive of ProfitMetrics, said: "In Regular Browsing, gclid is NOT stripped by default." Links opened from Mail and Messages did lose it. Simo Ahava was cautious: "It's possible Safari and iOS will start stripping click IDs when 26 is released. It's possible they won't." Separately, Safari 26 extended Advanced Fingerprinting Protection to all browsing, but that feature differs from the user-controlled Advanced Tracking and Fingerprinting Protection setting, which strips the GCLID only where it is switched on. Tracking specialist Luc Nugteren estimated in April 2026 that the default Private Browsing scope covers about 20% of Safari sessions, as PPC Land reported in coverage of Safari removing the GCLID. Nugteren's open-source "Restore GCLID" template, released on August 13, 2025, copies the value into a renamed parameter through a URL suffix.

Privacy researchers raise a sharper objection. A 2026 paper by Ha Dao, Abhishek Shinde, Sana Athar and Devashish Gosain, published in the Proceedings on Privacy Enhancing Technologies (PoPETs), found that "every ad click consistently carries a unique Google Click Identifier, gclid" on YouTube ads. Of 76 advertisers studied, 64 persisted it as a first-party cookie, and 55.4% still stored it after consent banners were rejected, according to the paper. Advertisers see the GCLID as an attribution tool; the researchers treat it as a persistent cross-site identifier.

Auto-tagging is the setting; the GCLID is what it produces. Switching auto-tagging off removes the GCLID entirely.

gbraid and wbraid are aggregated identifiers for iOS traffic. They cannot be tied to a single click or user, so they support modelled rather than click-level measurement.

UTM parameters are manual, human-readable tags (utm_source, utm_medium, utm_campaign) readable by any analytics tool. They describe a campaign; the GCLID identifies one specific click and means nothing without Google's records.

DCLID is the click identifier for Display & Video 360 and Campaign Manager 360, appended automatically for those platforms from September 30, 2024.

Recent developments

The plumbing around the GCLID is shifting. Google stopped accepting new session-attribute and IP-address implementations in Google Ads API conversion imports from February 2, 2026, as PPC Land reported when Google shut down session tracking for new advertisers. On June 15, 2026, the Ads API stopped accepting new adopters of offline conversion imports through ConversionUploadService.UploadClickConversions, pushing new integrations to the Data Manager API, which accepts up to 2,000 conversion events per request, as PPC Land covered when Google blocked new offline conversion imports via the Ads API. Existing users keep access. Google's stated preference for new adopters is enhanced conversions for leads, which matches hashed email addresses rather than click identifiers.

The GCLID is not being retired, but as of November 2026 it increasingly travels with gbraid, gad_ parameters and hashed first-party data.

Timeline

  • October 2000 - Google launches AdWords.
  • November 2005 - Google Analytics launches, built on the acquired Urchin product, with AdWords integration.
  • September 9, 2013 - Google's Ads Developer Blog documents the GclId field in the Click Performance Report.
  • March 2021 - Google introduces the wbraid parameter for iOS web conversions.
  • April 26, 2021 - Apple's App Tracking Transparency takes effect; Google stops sending GCLID for some iOS 14 app traffic.
  • May 2021 - Google introduces gbraid for iOS app conversions.
  • June 2022 - Firefox 102 adds query-parameter stripping.
  • June 2023 - Apple announces Link Tracking Protection for Safari 17, covering gclid.
  • September 30, 2024 - DCLID appended automatically for DV360 and CM360.
  • August 13, 2025 - Luc Nugteren releases the "Restore GCLID" Google Tag Manager template.
  • September 2025 - Safari 26 ships with Advanced Fingerprinting Protection for all browsing.
  • October 3, 2025 - gclid and gbraid can be populated together in one conversion upload.
  • December 9, 2025 - Google launches the Data Manager API.
  • February 2, 2026 - Ads API stops accepting new session-attribute and IP-address implementations.
  • 2026 - PoPETs paper documents GCLID persistence across 76 YouTube advertisers.
  • June 15, 2026 - Ads API closes offline conversion imports to new adopters.
  • July 16, 2026 - Google publishes a video explainer on the GCLID.
  • July 30, 2026 - Google Analytics adds an alert for missing gbraid and gad_ parameters.

Summary

Who: Google generates and resolves the GCLID; advertisers, agencies, analytics teams and CRM vendors capture and upload it. Browser makers, notably Apple and Mozilla, increasingly strip it.

What: A unique, opaque URL parameter attached to each Google Ads click by auto-tagging, used to tie online and offline conversions back to the click, campaign and keyword.

When: Launch date undocumented by Google; described in Google's developer documentation by September 2013, reshaped from 2021 by Apple's privacy changes and from 2026 by Google's shift to the Data Manager API.

Where: In the landing page URL, a first-party cookie on the advertiser's site, hidden form fields, CRM records and conversion uploads to Google Ads.

Why: Conversions happen away from the ad server. Without a click-level key, Google's automated bidding cannot learn which clicks produce sales, especially in long, offline sales cycles.